The evolutionarily conserved canonical Wnt/β-catenin signal transduction cascade controls many aspects of metazoan development. Context-dependent activation of the pathway is involved in embryonic cell fate decisions, stem cell regulation and tissue homeostasis (Clevers, H. Cell 2006, 127, 469-80).
A key feature of the Wnt/β-catenin pathway is the regulated proteolysis of the downstream effector β-catenin by the β-catenin destruction complex. The principal constituents of the β-catenin destruction complex are adenomatous polyposis coli (APC), Axin, and GSK3α/β. In the absence of Wnt pathway activation, cytosolic β-catenin is constitutively phosphorylated and targeted for degradation. Upon Wnt stimulation, the β-catenin destruction complex disassociates, which leads to the accumulation of nuclear β-catenin and transcription of Wnt pathway responsive genes.
Inappropriate activation of the pathway, mediated by over expression of Wnt proteins or mutations affecting components of the β-catenin destruction complex, thus leading to stabilization of β-catenin, has been observed in many cancers. Notably, truncating mutations of the tumour suppressor APC are the most prevalent genetic alterations in colorectal carcinomas (Miyaki, M. et al. Cancer Res 1994, 54, 3011-20; Miyoshi, Y. et al. Hum Mol Genet 1992, 1, 229-33; and Powell, S. M. et al. Nature 1992, 359, 235-7). In addition, Axin1 and Axin2 mutations have been identified in patients with hepatocarcinomas and colorectal cancer respectively (Taniguchi, K. et al. Oncogene 2002, 21, 4863-71; Liu, W. et al. Nat Genet 2000, 26, 146-7; Lammi, L. et al. Am J Hum Genet 2004, 74, 1043-50). These somatic mutations result in Wnt-independent stabilization of β-catenin and constitutive activation of β-catenin-mediated transcription.
Deregulated Wnt pathway activity has also been implicated in many other cancers (Polakis, P. Curr Opin Genet Dev 2007, 17, 45-51; and Barker, N. et al. Nat Rev Drug Discov 2006, 5, 997-1014), including colorectal, melanoma, breast, liver, lung and gastric cancers. Other disorders associated with aberrant Wnt signaling include osteoporosis, osteoarthritis, polycystic kidney disease, pulmonary fibrosis, diabetes, schizophrenia, vascular disease, cardiac disease, non-oncogenic proliferative diseases, and neurodegenerative diseases such as Alzheimer's disease.
The efficient assembly of the multi-protein β-catenin destruction complex is dependent on the steady state levels of its principal constituents. Axin has been reported to be the concentration-limiting factor in regulating the efficiency of the β-catenin destruction complex (Salic, A., et al. Mol Cell 2000, 5, 523-32; and Lee, E. et al. PLoS Biol 2003, 1, E10) and increased expression of Axin can enhance β-catenin degradation in cell lines expressing truncated APC (Behrens, J. et al. Science 1998, 280, 596-9; Kishida, M. et al. Oncogene 1999, 18, 979-85; and Hart, M. J., et al. Curr Biol 1998, 8, 573-81). Thus, it is likely that Axin protein levels need to be tightly regulated to ensure proper Wnt pathway signaling.
It has recently been found that β-catenin degradation can be promoted by stablising Axin through the inhibition of the poly-ADP-ribose polymerase (PARP) enzymes tankyrase 1 and tankyrase 2, as explained in WO 2009/059994 and Huang et al., (Huang S. M., et al. Nature 2009, 461, 614-620). Both tankyrase isoforms interact with a highly conserved domain of Axin and stimulate its degradation through the ubiquitin-proteasome pathway. This previously unknown mechanism for stabilising Axin protein, thereby enhancing β-catenin degradation, can be exploited for treating Wnt signaling-related disorders. Axin proteins are essential regulators of a spectrum of physiological processes, including brain oligodendrocyte progenitor cell differentiation for remyelination (Fancy, S., et al. Nature NeuroSci 2011, 14, 1009-1017), and epithelial-to-mesenchymal transition during pulmonary fibrosis (Ulsamer, A., et al. J Bio Chem 2012, 287, 5164-5172). Thus, by way of stabilizing Axin proteins, Tankyrase inhibitors could be used as a therapy for remyelination post brain injury and pulmonary fibrosis.
Tankyrase has several binding protein partners, including TRF1, a double-stranded telomeric repeat binding protein (Smith, S., et al. Science 1998, 282, 1484-1487); NuMA, an essential protein in mitotic spindle assembly (Chang, W., et al. Biochem J, 2005, 391, 177-184); IRAP, an integral membrane protein involved in glucose uptake in response to insulin (Chi, N. W., et al. J Biol Chem 2000, 275, 38437-38444); and Mcl-1, a pro-apoptotic protein (Bae, J., et al. J Biol Chem 2003, 278, 5195-5204).
By way of its various interacting proteins, tankyrase proteins have been implicated in different biological functions. Tankyrase poly (ADP-ribosyl)ates TRF1, releasing it from telomeres and enhancing telomere access to telomerase. Thus, tankyrase functions as a positive regulator for telomere elongation by telomerase, supported by the findings that long-term overexpression of tankyrase leads to telomere elongation (Cook, B. D., et al Mol Cell Biol 2002, 22, 332-242). Telomere maintenance by telomerase has been attributed to the uncontrolled proliferation of cancer cells (Hahn, W. C., et al, Nat Med 1999, 5, 1164-1169). Tankyrase could be a target for cancer therapy by inhibiting the telomere accessibility for telomerase. Tankyrase inhibition could be used as an effective cancer therapy to treat patients with a wide spectrum of cancers, including leukemia, lymphoma, multiple myeloma, lung, and breast cancer.
Tankyrase also plays a role in cell mitosis by: 1) poly(ADP-ribosyl)ating NuMA during mitosis and regulating its functions at spindle poles (Chang, W., et al. Biochem J 2005, 391, 177-184); 2) by regulating spindle assembly and structure (Chang, P., et al. Nature 2004, 432, 645-649); and 3) by maintaining sister chromatid resolution at telomeres (Dynek, J., et al. Science 2004, 304, 97-100). Inhibition of tankyrase leads to cell mitotic arrest or senescence, and thus could be exploited for treating diseases that have abnormal mitotic division, such as cancer. Examples include breast, lung, ovarian, leukemia, lymphoma, and melanoma. In addition, tankyrase 1 was identified as a gene required for centrosome clustering, a mechanism that cancer cells with supernumerary centrosomes employs to suppress multipolar mitosis and enable bipolar mitosis (Kwon, M., et al. Genes Dev 2008, 22, 2189-2203). Thus inhibition of tankyrase could be exploited for treating cancers with centrosome amplification, including both solid and haematological cancers, examples include breast, bladder, lung, colon, and leukemia.
Moreover, One of the cellular localizations of tankyrase is at the Golgi apparatus co-localizing with the glucose transporter GLUT4 vesicles where tankyrase is associated with IRAP, and tankyrase is implicated in the regulation of GLUT4 trafficking in adipocytes (Chi, N. W., et al. J Biol Chem 2000, 275, 38437-38444). Tankyrase-deficient mice exhibit reduced adiposity and increased energy expenditure by increases in both fatty acid oxidation and insulin-stimulated glucose utilization (Yeh, T., et al. Diabetes 2009). This supports tankyrase involvement in energy homeostasis in mammals and inhibiting tankyrase can be exploited for treating metabolic diseases, such as obesity.
Tankyrase has been reported to be a host protein targeted by Herpes Simplex Virus (HSV), modulated by HSV through hyperphosphorylation, nuclear transport and proteasomal degradation (Li Z., et al. J of Virol 2012, 86, 492-503). More importantly, efficient HSV viral replication requires the enzymatic activity of tankyrase proteins. Inhibition of tankyrase activity by inhibitor XAV939 (WO 2009/059994, Huang, S. M., et al. Nature 2009, 461, 614-620) suppressed HSV viral protein expression and decreased viral growth. Thus, inhibition of tankyrase can be exploited as anti-viral therapeutics, including but not limited to treatment of HSV infection.
Consequently, compounds that inhibit tankyrase (TNKS) and/or Wnt Signaling may be useful for treatment of diseases mediated by such inhibitions.